Purpose: This study will determine the effectiveness of the use of desensitivity gels prior in office bleaching on risk and intensity of tooth sensitivity caused by in-office bleaching using 35% hydrogen peroxide. Materials and Methods: Fifty patients will be selected for this triple-blind, randomized, cross-over, placebo-controlled clinical trial. 10 minutes prior to bleaching procedure, patients will receive the potassium oxalate 5% desensitivity gel and placebo application on vestibular surface. The whitening treatment with 35% hydrogen peroxide will be carried out in two sessions with a 7-day interval. Tooth sensitivity will be assessed before, during and 24 hours after the procedure using analog visual and verbal scales. Color alteration will be assessed by a Classical guide scale. Relative risk to sensitivity will be calculated and adjusted by session; while comparison of overall risk will performed by McNemar's test. Data on the sensitivity level for both scales and color shade will be subjected to the Friedman, Wilcoxon and Mann-Whitney tests, respectively (α = 0.05)